1. Field of the Invention
The invention relates to maintaining signal integrity in electrical assemblies, and more particularly to a crosstalk cancellation technique suitable for integrated circuit packaging configurations.
2. Description of the Related Art
As semiconductor packaging densities increase, crosstalk-between adjacent signal paths becomes an important noise factor that can limit performance of packaged integrated circuits. In particular, as high performance integrated circuits demand larger currents at higher frequencies with lower power supply voltages, inductively coupled crosstalk between adjacent signal paths (e.g., between pins or solder balls) may be sufficient to cause logic errors or necessitate noise tolerant circuit techniques. Accordingly, techniques are desired whereby the effects of crosstalk between adjacent signal paths, e.g., between adjacent signal paths in a Pin Grid Array (PGA), Ball Grid Array (BGA), etc., may be reduced.
One commonly used technique for canceling crosstalk in data connectors includes use of antiphase signal pairs and the cancellation of a primary crosstalk signal coupled from a first signal path of the pair using an antiphase crosstalk signal coupled from the second signal path of the pair. U.S. Pat. No. 5,679,027 describes one such technique applied to an RJ45 connecting system of plugs and jacks by exploiting capacitive coupling of conductors. U.S. Pat. No. 5,547,405 a similar approach to suppression of crosstalk in a telecommunications connector. Such techniques have also been employed in integrated circuit signal line systems such as differential bit line pairs of a semiconductor memory as shown in U.S. Pat. No. 5,475,643.
However, unlike telecommunications connectors and differential bit-line circuit designs, differential signal pairs are typically not available in semiconductor packaging configurations. As a result, crosstalk suppression techniques relying on equal and opposing coupling of antiphase voltages onto a signal line are inapposite. Furthermore, in many high performance packaged integrated circuit applications, inductively coupled crosstalk is dominant. Accordingly, other techniques are needed to address crosstalk issues presented by high-density semiconductor packaging technologies.